Uplink MAC protocol aspects

ABSTRACT

Methods of operation of a wireless device are provided. In particular, Media Access Control (MAC) protocol aspects are disclosed relating to Licensed Assisted Access (LAA) cells and, more generally, to cells of a cellular communications network operating in an unlicensed frequency spectrum. According to one aspect, a method of operation of a wireless device comprises transmitting an Uplink (UL) transmission on a cell for a corresponding UL Hybrid Automatic Repeat Request (HARQ) process, the cell operating in an unlicensed frequency spectrum, and setting a locally maintained status for the UL HARQ process to Acknowledgement (ACK) based on an assumption that the UL transmission was successful.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/364,800, filed Nov. 30, 2016, granted as U.S.Pat. No. 10,355,830 on Jul. 16, 2019, which claims the benefit ofprovisional patent application Ser. No. 62/264,075, filed Dec. 7, 2015,the disclosure of which are hereby incorporated herein by reference intheir entirety.

TECHNICAL FIELD

This disclosure is related to uplink Medium Access Control (MAC)protocol aspects, i.e., the functionality for transmitting data on ashared Uplink (UL) channel (e.g., Physical Uplink Shared Channel(PUSCH)) as well as transmission of Hybrid Automatic Repeat Request(HARQ) Acknowledgement/Negative Acknowledgement (ACK/NACK) feedback andscheduling request on a UL control channel (e.g., Physical UplinkControl Channel (PUCCH)) or on a shared UL channel (e.g., PUSCH).

BACKGROUND

Licensed Assisted Access (LAA) facilitates Third Generation PartnershipProject (3GPP) Long Term Evolution (LTE) equipment to operate in theunlicensed 5 gigahertz (GHz) radio spectrum. The unlicensed 5 GHzspectrum is used as a complement to the licensed spectrum. Devices canconnect in the licensed spectrum (using a Primary Cell (PCell)) and useCarrier Aggregation (CA) to benefit from additional transmissioncapacity in the unlicensed spectrum (using a Secondary Cell (SCell)). Toreduce the changes involved for aggregating licensed and unlicensedspectrum, the LTE frame timing in the PCell is simultaneously used inthe SCell.

Regulatory requirements, however, may not permit transmissions in theunlicensed spectrum without prior channel sensing. Since the unlicensedspectrum must be shared with other radios of similar or dissimilarwireless technologies, a so called Listen-Before-Talk (LBT) procedureneeds to be applied. Today, the unlicensed 5 GHz spectrum is mainly usedby equipment implementing the Institute of Electrical and ElectronicsEngineers (IEEE) 802.11 Wireless Local Area Network (WLAN) standard.This standard is known under its marketing brand “Wi-Fi.” In manyregions there is also a constraint on the maximum duration of a singletransmission burst in the unlicensed spectrum, such as 4 milliseconds(ms) or 10 ms.

1. LTE

FIG. 1A illustrates a basic LTE downlink physical resource grid. LTEuses Orthogonal Frequency Division Multiplexing (OFDM) in the downlinkand Discrete Fourier Transform (DFT) spread OFDM (DFT-spread OFDM),which is also referred to as single-carrier Frequency Division MultipleAccess (FDMA), in the Uplink (UL). The basic LTE downlink physicalresource can thus be seen as a time-frequency grid as illustrated inFIG. 1A, where each resource element corresponds to one OFDM subcarrierduring one OFDM symbol interval. The duration of each symbol isapproximately 71.4 microseconds (μs). The UL subframe has the samesubcarrier spacing as the Downlink (DL) and the same number of SingleCarrier FDMA (SC-FDMA) symbols in the time domain as OFDM symbols in theDL.

FIG. 1B illustrates an LTE radio frame. In the time domain, LTE DLtransmissions are organized into radio frames of 10 ms, each radio frameconsisting of ten equally-sized subframes of length T_(SUBFRAME)=1 ms asshown in FIG. 1B. For normal cyclic prefix, one subframe consists of 14OFDM symbols. A subframe is divided into two 0.5 ms slots. For normalcyclic prefix, each slot consists of 7 OFDM symbols. Furthermore, theresource allocation in LTE is typically described in terms of resourceblocks, where a resource block corresponds to one 0.5 ms slot in thetime domain and 12 contiguous subcarriers in the frequency domain. Apair of two adjacent resource blocks in time direction (1.0 ms) is knownas a resource block pair. Resource blocks are numbered in the frequencydomain, starting with 0 from one end of the system bandwidth.

FIG. 1C illustrates an example LTE 1.0 ms subframe (with 14 OFDMsymbols) showing the locations of control signals and reference signals.DL transmissions are dynamically scheduled, i.e., in each subframe thebase station transmits control information about which terminals data istransmitted to and upon which resource blocks the data is transmitted,in the current DL subframe.

This control signalling is typically transmitted in the first 1, 2, 3,or 4 OFDM symbols in each subframe and the number n=1, 2, 3, or 4 isknown as the Control Format Indicator (CFI). The DL subframe alsocontains common reference symbols, which are known to the receiver andused for coherent demodulation of, e.g., the control information. A DLsystem with CFI=3 OFDM symbols as control is illustrated in FIG. 1C.

From LTE Release 11 (Rel-11) onwards, the above described resourceassignments can also be scheduled on the enhanced Physical DownlinkControl Channel (EPDCCH). For LTE Rel-8 to Rel-10, only the PhysicalDownlink Control Channel (PDCCH) is available. The reference symbolsshown in FIG. 1C are the Cell specific Reference Symbols (CRSs) and areused to support multiple functions including fine time and frequencysynchronization and channel estimation for certain transmission modes.

1.1 PDCCH and EPDCCH

The PDCCH/EPDCCH is used to carry Downlink Control Information (DCI)such as scheduling decisions and power control commands. Morespecifically, the DCI includes:

-   -   DL scheduling assignments, including Physical Downlink Shared        Channel (PDSCH) resource indication, transport format, Hybrid        Automatic Repeat Request (HARQ) information, and control        information related to spatial multiplexing (if applicable). A        DL scheduling assignment also includes a command for power        control of the Physical Uplink Control Channel (PUCCH) used for        transmission of HARQ acknowledgements in response to DL        scheduling assignments.    -   UL scheduling grants, including Physical Uplink Shared Channel        (PUSCH) resource indication, transport format, and HARQ-related        information. A UL scheduling grant also includes a command for        power control of the PUSCH.    -   Power control commands for a set of terminals as a complement to        the commands included in the scheduling assignments/grants.

One PDCCH/EPDCCH carries one DCI message containing one of the groups ofinformation listed above. As multiple terminals can be scheduledsimultaneously, and each terminal can be scheduled on both DL and ULsimultaneously, there must be a possibility to transmit multiplescheduling messages within each subframe. Each scheduling message istransmitted on separate PDCCH/EPDCCH resources, and consequently thereare typically multiple simultaneous PDCCH/EPDCCH transmissions withineach subframe in each cell. Furthermore, to support different radiochannel conditions, link adaptation can be used, where the code rate ofthe (E)PDCCH is selected by adapting the resource usage for the(E)PDCCH, to match the radio channel conditions.

1.2 CA

FIG. 2 illustrates an example of CA. The LTE Rel-10 standard supportsbandwidths larger than 20 megahertz (MHz). One important aspect of LTERel-10 is to assure backward compatibility with LTE Rel-8. This shouldalso include spectrum compatibility. That would imply that an LTE Rel-10carrier, wider than 20 MHz, should appear as a number of LTE carriers toan LTE Rel-8 terminal. Each such carrier can be referred to as aComponent Carrier (CC). In particular for early LTE Rel-10 deployments,it can be expected that there will be a smaller number of LTERel-10-capable terminals compared to many LTE legacy terminals.Therefore, it is necessary to ensure an efficient use of a wide carrieralso for legacy terminals, i.e. that it is possible to implementcarriers where legacy terminals can be scheduled in all parts of thewideband LTE Rel-10 carrier. The straightforward way to obtain thiswould be by means of CA. CA implies that an LTE Rel-10 terminal canreceive multiple CCs, where the CCs have, or at least have thepossibility to have, the same structure as a Rel-8 carrier. CA isillustrated in FIG. 2. A CA-capable User Equipment device (UE) isassigned a PCell which is always activated, and one or more SCells whichmay be activated or deactivated dynamically.

The number of aggregated CCs as well as the bandwidth of the individualCC may be different for UL and DL. A symmetric configuration refers tothe case where the number of CCs in DL and UL is the same, whereas anasymmetric configuration refers to the case that the number of CCs isdifferent. It is important to note that the number of CCs configured ina cell may be different from the number of CCs seen by a terminal: Aterminal may for example support more DL CCs than UL CCs, even thoughthe cell is configured with the same number of UL and DL CCs.

In addition, a key feature of CA is the ability to perform cross-carrierscheduling. This mechanism allows a (E)PDCCH on one CC to schedule datatransmissions on another CC by means of a 3-bit Carrier Indicator Field(CIF) inserted at the beginning of the (E)PDCCH messages. For datatransmissions on a given CC, a UE expects to receive scheduling messageson the (E)PDCCH on just one CC—either the same CC, or a different CC viacross-carrier scheduling; this mapping from (E)PDCCH to PDSCH is alsoconfigured semi-statically. Note that cross-subframe cross-carrierscheduling of PDSCH is not supported in Rel-11 CA, i.e., the (E)PDCCHgrant in a particular subframe applies to a PDSCH allocation in thatsame Transmit Time Interval (TTI).

2. WLAN

FIG. 3 is a general illustration of an LBT mechanism. In typicaldeployments of WLAN, Carrier Sense Multiple Access with CollisionAvoidance (CSMA/CA) is used for medium access. The channel is sensed toperform a Clear Channel Assessment (CCA), and a transmission isinitiated only if the channel is declared idle. If the channel isdeclared busy, the transmission is essentially deferred until thechannel is deemed to be idle. When the range of several Access Points(APs) using the same frequency overlap, transmissions related to one APmight be deferred in case a transmission on the same frequency to orfrom another AP which is within range can be detected. If several APsare within range, they will have to share the channel in time, and thethroughput for the individual APs may be severely degraded.

3. LAA to Unlicensed Spectrum using LTE

Up to now, the spectrum used by LTE is dedicated to LTE (i.e., licensedspectrum). This has the advantage that the LTE system does not need tocare about the coexistence issue and the spectrum efficiency can bemaximized. However, the spectrum allocated to LTE is limited and, assuch, cannot meet the ever increasing demand for larger throughput fromapplications/services. Therefore, a new study item has been initiated in3GPP on extending LTE to exploit unlicensed spectrum in addition tolicensed spectrum. Unlicensed spectrum can, by definition, besimultaneously used by multiple different technologies. Therefore, LTEneeds to consider the coexistence issue with other systems such as IEEE802.11 (Wi-Fi). Operating LTE in the same manner in unlicensed spectrumas in licensed spectrum can seriously degrade the performance of Wi-Fi,as Wi-Fi will not transmit once it detects the channel is occupied.

Furthermore, one way to utilize the unlicensed spectrum reliably is totransmit essential control signals and channels on a licensed carrier.That is, a UE is connected to a PCell in the licensed band and one ormore SCells in the unlicensed band. As used herein, an SCell inunlicensed spectrum is denoted as an LAA SCell. In the case ofcross-carrier scheduling, PDSCH and PUSCH grants for the LAA SCell aretransmitted on the PCell.

Another way to utilize the unlicensed spectrum is to utilize standaloneLAA cells.

SUMMARY

This disclosure is related to uplink Medium Access Control (MAC)protocol aspects, i.e., the functionality for transmitting data on ashared Uplink (UL) channel (e.g., Physical Uplink Shared Channel(PUSCH)) as well as transmission of Hybrid Automatic Repeat Request(HARQ) Acknowledgement/Negative Acknowledgement (ACK/NACK) feedback andscheduling request on a UL control channel (e.g., Physical UplinkControl Channel (PUCCH)) or on a shared UL channel (e.g., PUSCH). Inparticular, MAC protocol aspects are disclosed herein relating toLicensed Assisted Access (LAA) cells and, more generally, to cells of acellular communications network operating in an unlicensed frequencyspectrum.

According to one aspect, a method of operation of a wireless devicecomprises transmitting a UL transmission on a cell for a correspondingUL HARQ process, the cell operating in an unlicensed frequency spectrum,and setting a locally maintained status for the UL HARQ process to “ACK”based on an assumption that the UL transmission was successful. In oneembodiment, the method further comprises performing a retransmission forthe uplink HARQ process only upon reception of a corresponding UL grantwith a New Data Indicator (NDI) not toggled.

According to another aspect, a method of operation of a wireless devicecomprises determining whether the wireless device has a valid UL grantin a subframe on a cell, the cell operating in an unlicensed frequencyspectrum, and starting a UL HARQ feedback timer upon determining thatthe wireless device has a valid UL grant in the subframe on the cell. Inone embodiment, the UL HARQ feedback timer is started whether thewireless device performs a corresponding UL transmission or whether thecorresponding UL transmission is blocked by a Listen-Before-Talk (LBT)scheme. In one embodiment, the method further comprises starting aDiscontinuous Reception (DRX) retransmission timer upon expiry of the ULHARQ feedback timer. In one embodiment, the method further comprisesremaining in DRX active time as long as the DRX retransmission timer isrunning. In one embodiment, the method further comprises stopping the ULHARQ feedback timer upon flushing a corresponding HARQ buffer. In oneembodiment, one uplink HARQ Round Trip Time (RTT) timer and one DRXretransmission timer are maintained per UL HARQ process.

According to another aspect, a method of operation of a wireless devicecomprises transmitting Uplink Control Information (UCI) on a celloperating in an unlicensed frequency spectrum, the UCI comprising HARQfeedback information for one or more Downlink (DL) HARQ processes, andidentifiers that identify the one or more DL HARQ processes. In oneembodiment, the one or more DL HARQ processes are identified by anexplicit identifier or by a bitmap wherein each bit corresponds to oneof the one or more DL HARQ processes. In one embodiment, the methodfurther comprises receiving feedback control information from a basestation serving the cell, the feedback control information comprising anindication of whether bundling of the DL HARQ feedback in a UCI is to beperformed. In one embodiment, the feedback control information furthercomprises information that indicates a number of DL HARQ feedbacks thatthe wireless device is to bundle in a UCI.

According to another aspect, a method operation of a wireless device ina network having a primary serving cell and a secondary serving cellcomprises: in response to receiving a DL transmission from a primaryserving cell, providing a HARQ feedback to the primary serving cell, andin response to receiving a DL transmission from a secondary servingcell, providing a HARQ feedback to the secondary serving cell instead ofto the primary serving cell. In some embodiments, each UL serving cellcarries HARQ feedback for a corresponding DL serving cell.

According to another aspect, a method of operation of a wireless devicecomprises determining whether the wireless device has a valid UL grantin a subframe on a cell, the cell operating in an unlicensed frequencyspectrum; upon determining that the wireless device has a valid ULgrant, multiplexing pending HARQ feedback onto a UL shared channel; andupon determining that the wireless device does not have a valid ULgrant, sending pending DL HARQ feedback on a UL control channel upon asuccessful short LBT operation. In one embodiment, the UL controlchannel is a long UL control channel.

According to another aspect, a method of operation of a wireless devicecomprises skipping UL LBT before a UL transmission in a subframe on acell operating in an unlicensed frequency spectrum if both the wirelessdevice performed a UL transmission in a preceding subframe and thewireless device received an explicit indication that skipping UL LBT ispermitted. In one embodiment, the UL transmission in the precedingsubframe was a PUSCH transmission. In one embodiment, the ULtransmission in the preceding subframe was a long PUCCH transmission.

According to another aspect, a method of operation of a wireless devicecomprises performing a UL LBT operation at the beginning of a ULsubframe rather than at the end of the preceding subframe.

According to another aspect, a method of operation of a wireless devicecomprises sending pending HARQ feedback on a short UL control channel ona cell operating in an unlicensed frequency spectrum if the wirelessdevice has received an indication of a shortened DL subframe. In oneembodiment, the wireless device does not need to perform LBT prior tosending the pending HARQ feedback on the short UL control channel. Inone embodiment, the method further comprises determining short ULcontrol channel resources on which to send the pending HARQ feedback. Inone embodiment, the wireless device determines the short UL controlchannel resources based on the Radio Resource Control (RRC)configuration and information contained within a DL assignment.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the embodiments in association withthe accompanying drawing figures.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the embodiments in association withthe accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 A illustrates a conventional example Orthogonal FrequencyDivision Multiplexing (OFDM) Downlink (DL) physical resource grid usedby Long Term Evolution (LTE);

FIG. 1B illustrates a conventional LTE radio frame showing the OFDMtime-domain structure;

FIG. 1C illustrates an example LTE 1.0 ms OFDM DL subframe (with 14 OFDMsymbols) showing the locations of control signals and reference signals;

FIG. 2 is a schematic diagram of an example of Carrier Aggregation (CA);

FIG. 3 is a schematic diagram showing of a Listen-Before-Talk (LBT)scheme;

FIG. 4A depicts an exemplary short Physical Uplink Control Channel(PUCCH) according to some embodiments of the subject matter describedherein;

FIG. 4B depicts an exemplary long PUCCH according to some embodiments ofthe subject matter described herein;

FIG. 5A depicts a high signalling overhead required for Uplink (UL)bursts using legacy UL grant transmission methods;

FIG. 5B depicts an example of UL grant multiplexing according to someembodiments of the present disclosure;

FIG. 6 depicts an example of Uplink Control Information (UCI) in aPhysical Uplink Shared Channel (PUSCH) where the User Equipment device(UE) has received DL data (on the Physical Downlink Shared Channel(PDSCH)) in four consecutive subframes as well as UL grants valid forthe four subsequent subframes according to some embodiments of thepresent disclosure;

FIG. 7 depicts a similar case to that of FIG. 6 but here the UCI fromthe UE having received PDSCH in the first four subframes is mapped to along PUCCH that spans across all available symbols of the subsequentfour subframes whereas the PUSCH resources are assumed to be allocatedto another UE;

FIG. 8 illustrates an example of an embodiment in which additional LBTphases are needed if different UEs provide their PUCCH feedback inadjacent subframes;

FIG. 9 illustrates a bundled PUCCH transmission according to someembodiments of the present disclosure;

FIG. 10 illustrates one example in which a short PUCCH (sPUCCH) islocated at the end of a shortened DL subframe;

FIG. 11 depicts an example where a UE is configured with a DedicatedScheduling Request (D-SR) opportunity in every fourth subframe;

FIGS. 12A and 12B illustrate examples of a cellular communicationsnetwork in which embodiments of the present disclosure may beimplemented;

FIG. 13 illustrates the operation of a base station and a wirelessdevice to implement proposal 3 according to some embodiments of thepresent disclosure;

FIG. 14 is a flow chart that illustrates the operation of a wirelessdevice to implement proposals 4-7 according to some embodiments of thepresent disclosure;

FIG. 15 illustrates the operation of a base station and a wirelessdevice to implement proposal 8 or 9 according to some embodiments of thepresent disclosure;

FIG. 16 is a flow chart that illustrates the operation of a wirelessdevice to implement proposal 11 according to some embodiments of thepresent disclosure;

FIG. 17 is a flow chart that illustrates the operation of a wirelessdevice to implement proposal 12 according to some embodiments of thepresent disclosure;

FIG. 18 illustrates the operation of a base station and a wirelessdevice to implement proposal 13 according to some embodiments of thepresent disclosure;

FIG. 19 illustrates the operation of a base station and a wirelessdevice to implement some or all of proposals 15-17 according to someembodiments of the present disclosure;

FIG. 20 illustrates the operation of a base station and a wirelessdevice to implement some or all of proposals 18-20 according to someembodiments of the present disclosure;

FIGS. 21 and 22 illustrate embodiments of a base station according tosome embodiments of the present disclosure;

FIGS. 23 and 24 illustrate embodiments of a wireless device according tosome embodiments of the present disclosure;

FIG. 25 illustrates the operation of a wireless device in a primaryserving cell and in a secondary serving cell according to someembodiments of the present disclosure; and

FIG. 26 illustrates an LBT operation being performed at the end of asubframe just prior to a UL subframe versus an LBT operation beingperformed at the beginning of a UL subframe according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent information to enable thoseskilled in the art to practice the embodiments and illustrate the bestmode of practicing the embodiments. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the disclosure and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

The embodiments set forth below represent information to enable thoseskilled in the art to practice the embodiments and illustrate the bestmode of practicing the embodiments. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the disclosure and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure.

Radio Node: As used herein, a “radio node” is either a radio access nodeor a wireless device.

Radio Access Node: As used herein, a “radio access node” is any node ina radio access network of a cellular communications network thatoperates to wirelessly transmit and/or receive signals. Some examples ofa radio access node include, but are not limited to, a base station(e.g., an enhanced or evolved Node B (eNB) in a Third GenerationPartnership Project (3GPP) Long Term Evolution (LTE) network), ahigh-power or macro base station, a low-power base station (e.g., amicro base station, a pico base station, a home eNB, or the like), and arelay node.

Wireless Device: As used herein, a “wireless device” is any type ofdevice that has access to (i.e., is served by) a cellular communicationsnetwork by wirelessly transmitting and/or receiving signals to a radioaccess node(s). Some examples of a wireless device include, but are notlimited to, a User Equipment device (UE) in a 3GPP LTE network and aMachine Type Communication (MTC) device.

Network Node: As used herein, a “network node” is any node that iseither part of the radio access network or the core network of acellular communications network/system.

Listen-Before-Talk (LBT): As used herein, “LBT” or an “LBT scheme” isany scheme in which a radio access node or wireless device monitors achannel in an unlicensed frequency spectrum to determine whether thechannel is clear (e.g., performs a Clear Channel Assessment (CCA))before transmitting on the channel.

LBT Cell: As used herein, an “LBT cell” is a cell that operates on achannel in an unlicensed frequency spectrum in which an LBT scheme mustbe performed before transmitting.

Licensed Assisted Access (LAA) Secondary Cell (SCell): As used herein,an “LAA SCell” is one type of LBT cell. In particular, an “LAA SCell” isan SCell in a LTE network, where the SCell operates in an unlicensedfrequency spectrum, with the assistance from another cell (i.e., PrimaryCell (PCell)) operating in a licensed frequency spectrum.

Standalone LBT Cell: As used herein, a “standalone LBT cell” is one typeof LBT cell (e.g., a cell in an LTE network) that operates on its ownwithout the assistance from another cell operating in a licensedfrequency spectrum. Note the the description given herein focuses on3GPP LTE and, as such, 3GPP LTE terminology is oftentimes used. However,the concepts disclosed herein are not limited to 3GPP LTE.

Note that, in the description herein, reference is made to the term“cell”; however, particularly with respect to Fifth Generation (5G)concepts, beams may be used instead of cells and, as such, it isimportant to note that the concepts described herein are equallyapplicable to both cells and beams. Thus, in some embodiments, thetransmissions described herein may be performed on beams rather thancells (e.g., a beam in an unlicensed frequency spectrum).

In this disclosure the Uplink (UL) related Medium Access Control (MAC)protocol aspects, i.e., the functionality required for transmitting dataon the Physical Uplink Shared Channel (PUSCH) as well as transmission ofHybrid Automatic Repeat Request (HARQ) Acknowledgement/NegativeAcknowledgement (ACK/NACK) feedback and scheduling request on thePhysical Uplink Control Channel (PUCCH) or PUSCH is investigated.

Realization of PUCCH on the Physical Layer

In the present disclosure, the physical layer design of PUCCH forstandalone LTE in Unlicensed Spectrum (LTE-U) operation is provided. Twooptions, short PUCCH (sPUCCH) and long PUCCH design, are described fromphysical layer perspective. The MAC protocol design of HARQ feedback andScheduling Request (SR) on PUCCH will be discussed below

The Uplink Control Information (UCI) including HARQ-ACK, SR, andperiodic Channel State Information (CSI) can be transmitted on PUCCH in3GPP LTE. For standalone operation in unlicensed band, two PUCCH formatscan be considered for UCI transmission depending on eNB timingconfiguration and HARQ protocol, as will be described below. It shouldbe noted that it is beneficial that each UL serving cell carries theHARQ feedback for the corresponding DL serving cell in standalone LTE-U.This avoids the channel status of one cell determining the HARQ-ACKfeedbacks of all cells. This approach is different from LTE wheretypically the PUCCH of the PCell carries the UCI for all SCells.However, in terms of channel utilization and PUCCH format design, it issuggested to have independent PUCCH for each standalone carrier.

Short PUCCH (sPUCCH)

A sPUCCH occupies 1-3 Single Carrier Frequency Division Multiple Access(SC-FDMA)/Orthogonal Frequency Division Multiplexing (OFDM) symbols intime domain, and spans the whole bandwidth by interlacing. As sPUCCH canbe transmitted in the end of a DL partial subframe or as a part of a ULsubframe (at least if the PUSCH is scheduled to the same UE). In orderto transmit sPUCCH, an aggressive LBT may be applied at UE.Alternatively, no LBT is required if sPUCCH duration is below 5% of theduty cycle according to regulatory requirements.

FIG. 4A depicts an exemplary sPUCCH according to an embodiment of thesubject matter described herein. In the embodiment illustrated in FIG.4A, the PUCCH occupies 2 SC-FDMA/OFDM symbols in time and one interlacein frequency domain. The Demodulation Reference Signal (DMRS) and datasymbol for PUCCH can be frequency multiplexed or time multiplexed asillustrated in the figure as two options. Multiple PUCCH UEs can bemultiplexed in the frequency domain by assigning different interlacingpatterns and/or in the code domain by applying, for example, differentOrthogonal Cover Codes (OCCs) within a single interlace. The number ofsymbols, interlacing patterns, and OCC configuration (if any) can beconfigured for a UE by eNB signalling.

The HARQ feedback and the corresponding process Identifiers (IDs) couldeither be listed explicitly or, e.g., be provided as a bitmap (one ortwo bits per process). To align the design with 3GPP Release 13 (Rel-13)Carrier Aggregation (CA), the UCI on sPUCCH is attached with an 8-bitCyclic Redundancy Check (CRC) and encoded using Tail BitingConvolutional Code (TBCC). The encoded symbols are mapped to availableResource Elements (REs) in a frequency first time second manner.

Long PUCCH

A long PUCCH occupies a full subframe in time domain, and spans thewhole bandwidth by interlacing. A long PUCCH can be explicitly scheduledby eNB where LBT is required at UE to get access to the UL channel. Thelong PUCCH is compatible and can be multiplexed with PUSCH transmissionfrom the same or different UEs.

FIG. 4B depicts an exemplary long PUCCH according to an embodiment ofthe subject matter described herein. In the embodiment illustrated inFIG. 4B, the PUCCH occupies one interlace in one subframe. There is oneDMRS per slot occupying the whole bandwidth in frequency, which can bemultiplexed with PUSCH DMRS by applying different cyclic shifts. Similarto sPUCCH, multiple PUCCH UEs can be multiplexed in the frequency domainby assigning different interlacing patterns and/or in the code domain byapplying, for example, different OCCs within a single interlace. Theremaining interlaces within the same subframe can be used for PUSCHtransmission and PUCCH/PUSCH transmission from other UEs. The interlacepattern, cyclic shift (CS), and OCC configuration (if any) can beconfigured for a UE by eNB signalling.

Similarly as sPUCCH, the HARQ feedback and the corresponding process IDscould either be listed explicitly or, e.g., be provided as a bitmap (oneor two bits per process) on long PUCCH.1 The UCI on long PUCCH isattached with an 8-bit CRC and encoded using TBCC. The encoded symbolsare mapped to available REs in a frequency first time second manner.

In 3GPP LTE, the UCI transmission on PUCCH includes HARQ-ACK, SR andperiodic CSI. For standalone LTE-U, it would be difficult to supportperiodic CSI and hence aperiodic CSI feedback is more essential andshould be supported on PUSCH scheduled by UL grant with or without ULShared Channel (UL-SCH) data. If more than one UCI type is transmittedon PUCCH, e.g. HARQ and SR in the same subframe, they are concatenated,jointly encoded and sent on either sPUCCH or long PUCCH format accordingto the eNB configuration based on DL HARQ protocol as will be describedbelow.

Uplink Listen-Before-Talk Algorithms

Rel-13 LAA UL LBT

Several aspects of UL LBT were discussed during Rel-13. With regard tothe framework of UL LBT, the discussion focused on the self-schedulingand cross-carrier scheduling scenarios.

It was recognized that UL LBT imposes an additional LBT step for ULtransmissions with self-scheduling, since the UL grant itself requires aDL LBT by the eNB. Therefore, Rel-13 LAA recommends that the UL LBT forself-scheduling should use either a single CCA duration of at least 25μs (similar to a DL Dedicated Reference Signal (DRS)), or a randombackoff scheme with a defer period of 25 μs including a defer durationof 16 μs followed by one CCA slot, and a maximum contention window sizechosen from X={3, 4, 5, 6, 7}. These options are also applicable forcross-carrier scheduling of UL by another unlicensed SCell.

A short UL LBT procedure for the case involving cross-carrier schedulingby a licensed PCell remains open for further study. The other option onthe table is a full-fledged random backoff procedure similar to thatused by Wi-Fi stations.

Finally, the case of UL transmissions without LBT when a UL transmissionburst follows a DL transmission burst on that respective carrier (with agap of at most 16 μs between the two bursts) was left open for furtherstudy in Rel-14.

Standalone UL LBT algorithm

It is essential that the standalone UL LBT design is compatible withprospective UL LAA LBT algorithms specified in Rel-14 LAA. Furthermore,the UL channel access needs to be competitive when compared to thedownlink. These aspects lead to the following proposals. Thus, thepresent disclosure proposes to retain the Rel-13 LAA UL LBT options as abasis for further study and proposes that the UL CCA Energy Detection(CCA-ED) threshold be at least as high as the DL CCA-ED threshold.

UL Grant Transmission

In legacy UL grant transmission, each UL subframe is scheduled by adedicated grant sent 4 ms earlier. This leads to a high signallingoverhead since 4 consecutive subframes with a UL grant are needed toindicate a single 4 ms UL burst, as seen in FIG. 5A.

FIG. 5A depicts the high signalling overhead required for UL burstsusing legacy UL grant transmission methods. At low loads, this furtherimplies that DL LBT would need to be performed just to send a UL grantwithout data in that subframe, which leads to inefficient usage of theunlicensed channel. The 4 ms delay between UL grant transmission and ULtransmission also makes it difficult to have a short DL burstimmediately followed by a UL burst.

The drawbacks of the legacy UL grant transmission reduce the potentialof UL LAA significantly but can be addressed with simple improvements,such as scheduling multiple UL subframes from a single DL subframe, andreducing the minimum delay between the UL grant reception and the ULsubframe. These will now be addressed in turn.

Multi-subframe scheduling. Scheduling multiple UL subframes from asingle DL subframe reduces the signalling overhead for UL LAA and theinterference caused to neighboring cells. For a low load situation withonly UL traffic at a given time, if it is possible to schedule 4 ULsubframes from within a DL subframe, the overhead of the granttransmission is reduced to 25%. The reduction in overhead could besomewhat smaller, if it is possible to indicate different configurationsin the individual sub-frames. We might want to change Modulation andCoding Scheme (MCS), interlaces, Sounding Reference Signal (SRS)configurations, DMRS configurations, and so on. This feature is alreadysupported in Time Division Duplexing (TDD), since configuration 0 with 3UL subframes for 2 DL subframes supports scheduling multiple ULsubframes from a single DL subframe. If the number of scheduled ULsubframes with a DL subframe is further increased, e.g. to 12, thesignalling overhead can be further reduced, e.g. to 8.33%, and the LAAUL performance further improved. However, the optimal number ofscheduled UL subframes with the same DL subframe depends on manyfactors, such as traffic type, traffic load and UE buffer size.Therefore, the eNB should ideally have the freedom to configure how manyUL subframes are scheduled with the same DL subframe. The MAC protocolimpact is minimal, as discussed below. Thus, another proposal of thepresent disclosure is to support multi-subframe scheduling for UL.

Reduced UL grant delay. To further improve the uplink performance, thelegacy fixed UL grant delay of 4 ms should be reduced. Considering alow-load situation with only UL traffic at a given time, if UL grantmultiplexing alone is applied without further optimization, one can endup with the situation depicted in FIG. 5B.

FIG. 5B depicts an example of UL grant multiplexing according to anembodiment of the present disclosure. The signalling overhead of the ULgrant transmission is reduced, but instead of using previous UL grantsubframes for UL data transmission, they are simply kept empty until ULtransmissions commence. Thus, the uplink throughput remains limited.

The eNB scheduling may be optimized so as to avoid as far as possiblethe situation depicted in FIG. 5B. Nevertheless, this situation willoccur each time the multiplexed UL grants transmission cannot occur inthe planned subframe due to LBT failure. The most natural andstraight-forward method to solve the issue in FIG. 5B is to reduce thegrant delay for the uplink. Thus, another proposal of the presentdisclosure is to reduce the delay between the UL grant and thecorresponding UL transmission to less than 4 ms.

Uplink HARQ for PUSCH

Proposal 1: Adopt asynchronous UL HARQ

In section 7.2.2.2 of the LAA study item phase 3GPP Technical Report(TR) 36.889 V13.0.0, “[a]synchronous HARQ is recommended for LAA UL,”specifically for the PUSCH. That means UL retransmissions may not onlyoccur one Round Trip Time (RTT) (e.g., n+8) after the initialtransmission but rather at any point in time. This is consideredbeneficial in particular when (re-) transmissions are blocked andpostponed due to LBT. Thus, in order to maintain alignment with 3GPPRel-14 functionality, the present disclosure proposes to adoptasynchronous UL HARQ (as agreed in Rel-13 Study Item (SI) for LAA UL).

Proposal 2: Non-Adaptive Uplink HARQ is not supported

It was also agreed in section 7.2.2.2 of 3GPP TR 36.889 V13.0.0 that“with the UL asynchronous HARQ protocol, all transmission orretransmission should be scheduled via [Physical Downlink ControlChannel (PDCCH)] or [Enhanced PDCCH (ePDCCH)].” In other words,non-adaptive HARQ is no longer supported as it would not fit well to theconcept of asynchronous HARQ and it would require a reliable channel forcarrying the ACK/NACK in DL. As used herein, the term “non-adaptiveHARQ” refers to the mode of operation wherein a NACK on Physical HARQIndicator Channel (PHICH) triggers HARQ retransmission one RTT afterinitial transmission on same frequency resource with the same MCS. PHICHcould not be used as is: If the ACK on PHICH is blocked by LBT, the UEwould perform a non-adaptive retransmission according to existing HARQpattern and scheduling allocation. Thus, the present disclosure proposesthat non-adaptive UL HARQ not be supported.

Proposal 3: Assume that UL HARQ was Successful, Set Status to ACK

When introducing asynchronous HARQ, the UE should therefore assume thatall transmitted UL HARQ processes were successful (set local status toACK). The UE performs a HARQ retransmission for a HARQ process only uponreception of a corresponding UL grant (New Data Indicator (NDI) nottoggled) from the eNB. The process index is indicated in the HARQprocess index field in the UL grant. Note that this is also efficientconsidering that most transmission attempts are successful anyway andhence no feedback (PHICH) is needed anymore. Thus, the presentdisclosure proposes that upon transmission of a UL HARQ process the UEassumes that it was transmitted successfully and sets the locallymaintained status to ACK. The UE performs a HARQ retransmission for a ULHARQ process only upon reception of a corresponding UL Grant.

3GPP TR 36.889 V13.0.0 also mentions the need to introduce new means toflush a UL HARQ buffer. So far this happened with a counter per HARQprocess (CURRENT_TX_NB) which the UE incremented once per RTT, i.e.,whenever the process had a chance to be retransmitted. With theintroduction of asynchronous HARQ the retransmissions may happen atother points in time. It was therefore discussed in 3GPP that it may bemore appropriate to use a timer/counter that determines the number ofsubframes since the initial transmission of a process and flushes theprocess when the timer/counter exceeds a configured threshold. Butwhether or not it is necessary to flush the HARQ process depends, e.g.,on how the Discontinuous Reception (DRX) is handled.

The 3GPP study also identified the need to redefine the DRX Active Time:The UE needs to determine in which subframes it shall monitor PDCCH inorder to receive potentially incoming UL grants for HARQretransmissions. Since retransmissions for a particular HARQ process areno longer bound to specific subframes, grants for UL retransmissionsmay, in principle, appear in any subframe for any process that has notyet been flushed. Therefore, a simple solution would be to change thecondition in 3GPP TS 36.321, V 12.7.0 from “an uplink grant for apending HARQ retransmission can occur and there is data in thecorresponding HARQ buffer” to “there is data in any of the uplink HARQbuffers” and to flush the buffers as outlined in the previous paragraph.However, this approach would keep the UE awake continuously for a fairlylong time after each UL transmission even if no retransmissions arerequired.

Proposal 4: The UE Starts an “Uplink HARQ Feedback Time” in a SubframeWhere it has a Valid UL Grant

Due to the introduction of asynchronous HARQ it is fortunately no longernecessary to keep the UE awake continuously. The eNB is allowed toschedule a retransmission for any UL HARQ process in any subframe(provided that LBT succeeded). It is therefore suggested that aprinciple be used similar to the HARQ RTT Timer and aDRX-RetransmissionTimer that have been used for DL HARQ since Rel-8. Thedifference is that a timer, referred to herein as a “UL HARQ FeedbackTimer,” starts in the subframe when the UL grant becomes valid—both ifthe transmission takes place as well as if it was blocked byunsuccessful LBT. The UL HARQ Feedback Timer runs until the earliestpoint in time when a UL grant for a retransmission may be received.Thus, the present disclosure proposes that the UE starts a UL HARQFeedback Timer in a subframe where it has a valid UL grant, i.e., ifeither the UL transmission happens as well as if it is blocked by LBT.

Proposal 5: The UL HARQ Feedback Timer triggers a DRX-RetransmissionTimer

The present disclosure proposes that upon expiry of the UL HARQ FeedbackTimer, the UE starts a corresponding DRX-Retransmission Timer andremains in Active Time as long as said DRX-Retransmission Timer isrunning.

Proposal 6: Flushing the HARQ Buffer Stops the UL HARQ Feedback Timer

The present disclosure further proposes that the UE stops the UL HARQFeedback Timer upon flushing the corresponding HARQ buffer.

Proposal 7: One UL HARQ RTT Timer and one DRX-Retransmission Timer perUL HARQ Process

The present disclosure also proposes that one UL HARQ RTT Timer and oneDRX-Retransmission Timer are associated with each UL HARQ process.

However, it is noted that if proposals 4-7 are agreeable, there is nostrong need to flush UL HARQ buffers; thus, the present disclosure doesnot propose introducing such means for the time being. Alternatively,the present disclosure proposes that, where proposals 4-7 are adopted,flushing of UL HARQ buffers need not be done.

In the scope of the LAA study item, it has also been discussed tosupport multi-subframe scheduling so that the eNB could send UL grantsfor several PUSCH transmissions in a single DL subframe. Thisenhancement is considered useful as it maximizes resource utilizationand throughput whenever the traffic is UL heavy. Currently, theinteractions between L1 and MAC are modelled in a way that L1 takes careof the timing of grants and assignments. If a DCI comprises two ULgrants (e.g., for TDD), L1 provides them in the two appropriatesubframes to MAC. Assuming that the same modelling is applied, themulti-subframe UL scheduling is not expected to have any additionalimpact on the MAC specification. Note that the UL HARQ Feedback Timersuggested in proposals 4-7 ensures that the UE wakes at the earliesttime when a retransmission for any of those UL processes may occur.

UL Feedback for DL HARQ

The DL HARQ protocol is already asynchronous since 3GPP Rel-8 and henceready for use by LAA where the HARQ feedback (ACK/NACK) can be sentreliably on the PUCCH of a licensed PCell. However, for standaloneoperation (e.g., for a standalone LAA cell) (as well as for LAA withdual connectivity) the Uplink Control Information (UCI) is transmittedon unlicensed spectrum. As of today, regulatory rules allow to omit LBTfor control information (not for user plane data) if those transmissionsdo not occupy the medium for more than 5% of the time. While it would beattractive from a protocol point of view to design the PUCCH based onthis rule, the resulting collisions could impact the system performancenegatively. Furthermore, it is not unlikely that there are attempts tomodify or disallow this 5% rule. Therefore, it is proposed toinvestigate applying LBT to control signalling such as UCI.

Proposal 8:The UCI identifies the DL HARQ process(es)

As of today, the LTE DL HARQ design relies solely on the fixed timingrelation between the DL HARQ process and the corresponding HARQfeedback. Due to LBT, the time between DL transmission and HARQ feedbackwill vary and it is therefore considered necessary to include the HARQprocess ID in the HARQ feedback sent in the UL.

Since any kind of bundling increases the RTT, immediate feedback (insubframe n+4) is generally preferable. However, it also requires the eNBand the UE to switch the transmission direction (DL to UL, UL to DL)more frequently which increases the overhead. If the HARQ process IDneeds to be included in the HARQ feedback anyway, it is easily possibleto bundle HARQ feedback for multiple DL processes into a single ULmessage. The HARQ feedback and the corresponding process IDs couldeither be listed explicitly or be provided as a bitmap (one bit perprocess or per transport block). Thus, the present disclosure proposesthat the UCI contains the DL HARQ process identifiers either explicitlyor as a bitmap.

Proposal 9: The eNB Controls Whether and How Many HARQ Feedbacks the UEBundles in a UCI

While immediate feedback per process reduces the latency observed on theInternet Protocol (IP) layer, the feedback bundling improves thespectral efficiency. Which of these “modes” is preferable depends, e.g.,on the system load and on the queue of the particular UE. Therefore, theeNB should have means to switch between the modes, i.e., request HARQfeedback frequently or let the UE bundle feedback for multipleprocesses.

Proposal 10: Each UL Serving Cell Carries the HARQ Feedback for theCorresponding DL Serving Cell

As discussed in the section above titled “Realization of PUCCH on thePhysical Layer,” it is suggested that each UL serving cell carries theHARQ feedback for the corresponding DL serving cell. This is differentfrom LTE where typically the PUCCH of the PCell carries the UCI for allSCells, but in terms of channel utilization and PUCCH format design itis suggested to keep it separate in LTE unlicensed standalone.

This request could be either explicit as part of the DL assignment orthe UE could determine it based on the availability of appropriateresources for sending UCI. The details may vary and may also depend onthe PUCCH design(s), which are discussed below.

The provisioning of ACK/NACK feedback for downlink HARQ processes isfocused on here, but beyond that also Dedicated Scheduling Request(D-SR) and/or CSI needs to be transmitted.

Proposal 11: A UE with Valid UL Grant Multiplexes Pending HARQ (andPossibly Other UCI) Onto PUSCH

In principle, it should be possible to transmit HARQ feedback (UCI) inthe same subframe as PUSCH from the same UE, the same subframe as PUSCHfrom another UE, the same subframe as Physical Downlink Shared Chanel(PDSCH) for the same UE, the same subframe as PDSCH for another UE, oran empty subframe (UE did not receive UL grant nor detect PDSCH).

If a UE has a valid PUSCH grant, it is desirable to map the UCIinformation (if any is available) onto those PUSCH resources rather thanusing additional resource elements. As in LTE, this mapping to PUSCHoffers preferable transmission characteristics compared to assigningadditional resource elements for a PUCCH, such as a better cubic metric.

FIG. 6 depicts an example of UCI in PUSCH where the UE has received DLdata (PDSCH) in four consecutive subframes as well as UL grants validfor the four subsequent subframes according to an embodiment of thesubject matter described herein. While it would be possible to bundlethe HARQ feedback (e.g., into the last PUSCH subframe) it is preferableto send the HARQ feedback as early as possible. And since the UE has ULresources assigned anyway, the mapping shown below appears preferable.Thus, the present disclosure proposes that a UE with a valid UL grantmay multiplex pending HARQ and possibly other UCI onto a PUSCH.

Proposal 12: A UE Without Valid UL Grant Sends Pending HARQ Feedback on(long) PUCCH Upon Successful Short LBT

FIG. 7 depicts an example of UCI in PUSCH according to anotherembodiment of the subject matter described herein. FIG. 7 depicts a casesimilar to the one in FIG. 6, but in the embodiment illustrated in FIG.7, the UCI from the UE having received PDSCH in the first four subframesis mapped to a (long) PUCCH that spans across all available symbols ofthe subsequent four subframes whereas the PUSCH resources are assumed tobe allocated to another UE.

While the PUSCH transmission resources are granted explicitly, it isassumed that the UE derives the PUCCH resources implicitly from the DLgrants by similar mappings as defined in LTE. Before performing thePUCCH transmission, the UE has to perform LBT. As discussed for PUSCH inthe Rel-13 study item, it is considered possible to perform just a shortLBT since the preceding PDSCH transmission was subject to a regular LBT.In other words, the PUCCH uses the same LBT parameters as the scheduledPUSCH which allows multiplexing the transmissions in a single subframe.

In the example in FIG. 7, the UE has to shorten the fourth PUCCHtransmission so that the eNB could perform DL LBT prior to a subsequentDL subframe. This implies that upon scheduling UL resources for subframe8, the eNB also needs to decide whether the subsequent subframe 9 isgoing to be a UL or a DL subframe. If a DL subframe is supposed tofollow, the preceding UL subframe needs to end earlier. While thisconstraint is considered to be undesirable, it follows the baselineestablished in Rel-13. The eNB could use the PDCCH broadcast signallingthat was introduced in LAA Rel-13 to indicate shortening of thesubframe. Alternatively, it could provide this information as part ofthe DL assignment.

Proposal 13: Skipping UL LBT

FIG. 8 illustrates an example according to another embodiment of thesubject matter described herein in which additional LBT phases areneeded if different UEs provide their PUCCH feedback in adjacentsubframes. In addition to the LBT upon the DL-to-UL and UL-to-DLtransitions, additional LBT phases are needed if different UEs providetheir PUCCH feedback in adjacent subframes. This is highlighted in FIG.8 where a first UE receives PDSCH in the first two subframes and asecond UE receives PDSCH in the third and fourth subframes. While theeNB may perform the DL transmissions back-to-back, the second UE needsto sense the channel to be empty before performing its PUCCHtransmission.

When comparing the examples in Figure land FIG. 8, it becomes apparentthat a UE cannot determine by itself whether to perform LBT at thebeginning of a UL subframe. Even if it did use the preceding subframefor a UL transmission, it may have to do another LBT prior to thesubsequent subframe, depending whether or not other UEs need to performLBT in that subframe. Therefore, it is suggested that the eNB indicatesexplicitly in UL grants (for PUSCH) and DL assignments (for PUCCH)whether the UE may skip LBT for the corresponding UL subframe. In orderto avoid error cases, the UE should perform (short) LBT in a scheduledUL subframe if it had not performed a UL transmission in the precedingsubframe. This mismatch could have occurred due to the UE's LBT in thepreceding subframe, or due to missing a UL grant or DL assignment. Thus,the present disclosure proposes that a UE may skip its UL LBT if bothconditions are fulfilled: 1) the UE had performed a UL transmission(PUCCH or PUSCH) in the preceding subframe; and 2) the eNB explicitlypermitted skipping LBT in the UL grant or DL assignment.

It is also worth pointing out that, in the examples of FIG. 7 and FIG.8, the UE does not (need to) know whether its PUCCH transmissioncoincides with a PUSCH transmission of another UE. In other words, theproposals 2 and 5, above, are equivalent from the viewpoint of the UEtransmitting the PUCCH.

Proposal 14: The UE Performs UL LBT at the Beginning of the UL SubframeRather Than at the End of the Preceding Subframe

In Rel-13 LAA, it was decided that the eNB performs DL LBT prior to thestart of a DL subframe and that it shortens the last PDSCH subframe of aDL burst to make room for a subsequent LBT. Similarly, one couldconsider shortening the last UL transmission (PUSCH or PUCCH) of a UE.Then, a UE should also perform UL LBT prior to its UL subframe. However,this approach has significant drawbacks: it requires that the eNB doesnot only decide whether the subsequent subframe will also be a ULsubframe (see discussion above), but also whether it will be allocatedto the same or another UE. If so, the current subframe can span theentire subframes; if not, the current subframe has to be shortened. Such“look-ahead” is processing heavy and increases the scheduling delay.Secondly, it would be desirable that the eNB has a chance to win LBTagainst one of its UEs that intend to transmit PUCCH. For these reasonsthe present disclosure proposes performing UL LBT at the beginning of aUL subframe rather than at the end of the preceding subframe.

Proposal 15: A UE Sends Pending HARQ Feedback (and Possibly other UCI)on sPUCCH if the eNB Indicates a Shortened DL Subframe

Earlier in this disclosure the concept of feedback bundling wasintroduced. In the example of FIG. 7, the UE provides its HARQ feedbackas early as possible (i.e., n+4), which is desirable in terms oflatency. If the subframes are used for PUSCH transmissions of other UEsanyway, the additional overhead due to immediate HARQ feedback isnegligible. If, however, the eNB does not need the intermediatesubframes, it would be desirable to leave those empty and to let the UEbundle the HARQ feedback within a single PUCCH transmission.

FIG. 9 illustrates a bundled PUCCH transmission according an embodimentof the subject matter described herein. Since the bundling is consideredto be a special case, it is suggested that the eNB instructs the UE inthe DL assignment to postpone the HARQ feedback. In the example of FIG.9, it provides this indication in the first three downlink subframes andhence the UE omits PUCCH in subframes 5, 6, and 7. At the beginning ofsubframe 8, it performs (short) LBT and sends the pending HARQ feedbackfor all four DL HARQ processes.

Today, the user traffic is DL heavy. Hence, there will be many occasionsin which the eNB intends to schedule more DL than UL subframes.

Spending entire subframes for PUCCH would create an undesirableoverhead. It is therefore suggested to provide a short PUCCH in additionto the long PUCCH described here so far. This sPUCCH may appear at theend of a shortened DL subframe as shown in FIG. 10.

FIG. 10 illustrates an example in which a sPUCCH is located at the endof a shortened DL subframe according to an embodiment of the subjectmatter herein. The subframes 1, 2, 3 and 5, 6, 7 instruct the UE topostpone its HARQ feedback. The assignments in subframes 4 and 8 don'thave this indication and as a consequence the UE attempts to transmitUCI in subframe 8 (reflecting HARQ feedback for subframes 1-4) and insubframe 12 (reflecting HARQ feedback for subframes 5-8). If the UEwould find those subframes to be empty or if it would receive a PUSCHgrant for any of those subframes, it would provide the UCI feedback asdescribed in the previous paragraphs. But in this example, the eNBdecided to use these subframes primarily for DL data transfer. Insubframes 7 and 11 it notifies all UEs via the PDCCH broadcastsignalling that the subframes 8 and 12 will be shortened. The UE(s) withpending HARQ feedback will hence send that feedback on the sPUCCH.

Thus the present disclosure proposes that a UE may send pending HARQfeedback (and possibly other UCI) on an sPUCCH if the eNB indicates ashortened DL subframe.

Proposal 16: The UE Does Not Need to Perform LBT Prior to Transmissionof sPUCCH

Since the UCI is purely control signalling and since it follows directlyafter the eNB's DL transmission, the UE does not perform any LBT priorto the transmission. Of course, the eNB had to perform LBT at thebeginning of that DL burst.

Proposal 17: The UE Determines the sPUCCH Resources Based on the RadioResource Control (RRC) Configuration in Combination with the Received DLAssignment (similar to PUCCH)

If the subframe following the sPUCCH is scheduled for PUSCH, those UEswill perform (short) LBT in the beginning of that UL subframe. If theeNB intends to continue with a PDSCH transmission after the sPUCCH itmay do so after a short gap. This should occur in the end of the sPUCCH.As mentioned above, the eNB will thereby get the channel back and mayprevent its UEs from sending regular PUCCH in the subsequent subframe.

Similarly to PUCCH, the UE determines the sPUCCH resources based on theRRC configuration in combination with the received DL assignment.

D-SR

Proposal 18: The Network may Configure the UE with D-SR Resources UsingRRC Signalling

In LTE, the eNB typically configures a UE that is RRC connected with aD-SR resource on PUCCH. The periodicity (e.g., 10, 20, 40 subframes) aswell as the actual time/frequency resource is configured semi-staticallyvia RRC. Upon arrival of data (IP packets) from a higher layer into theUEs empty Packet Data Convergence Protocol (PDCP) queue, a Buffer StatusReport (BSR) is triggered. If the UE does not have a valid UL grant forsending the BSR, it sends a D-SR at its next D-SR occasion using PUCCH.The same principle could also be applied for LTE unlicensed standalone.However, it may be assumed that the UE performs LBT prior to thetransmission of the D-SR on PUCCH.

Proposal 19: The UE May Send D-SR in Those Occasions on PUCCH AfterSuccessful LBT

FIG. 11 depicts an example where a UE is configured with a D-SRopportunity in every fourth subframe according to an embodiment of thesubject matter described herein. At times when none of the UEs connectedwith the eNB are actively transmitting or receiving data, the eNBminimizes DL transmissions (DRS only) and most subframes will be empty.In this example, the UE attempts to send a D-SR in the third depictedD-SR occurrence and succeeds in doing so after successful LBT in thebeginning of the subframe.

Proposal 20: The UE May Send D-SR in Those Occasions on sPUCCH if theeNB Announces the Subframe to be a Shortened DL Subframe

Once the channel is occupied by UL or DL data transmissions, the UE'sLBT prior to D-SR is likely to fail due to ongoing PDSCH/PUSCH databursts. However, what might appear as a problem at a first glance isactually a desirable property: By using a more aggressive LBTconfiguration (still fair to Wi-Fi) than its UEs, the eNB can grab thechannel and schedule PDSCH/PUSCH efficiently as soon as data becomesavailable. To ensure that UEs can inform the eNB about available data,the eNB should declare at least some of the UEs' D-SR occasions asshortened DL subframes or leave them empty. As shown in the latter partof the sequence in FIG. 11, the UE will use those occasions for sendingD-SR (and HARQ feedback).

While there is a need to multiplex HARQ feedback onto the UE's PUSCHresources, there is no need to do that with D-SR. The reason is that aUE having a valid UL grant will rather include a (more detailed) bufferstatus report inside the MAC Protocol Data Unit (PDU) sent on PUSCH.

CSI

Besides HARQ feedback and D-SR, PUCCH also carries the CSI. In LTE itcan be mapped to PUCCH as well as to PUSCH.

Proposal 21: As Baseline, only Aperiodic CSI Feedback is Supported. Itis Mapped to PUSCH in Accordance with the UL Grant Provided by the eNB

As discussed in the section above titled “Realization of PUCCH on thePhysical Layer,” the aperiodic CSI reporting is considered important.Like in LTE, the aperiodic CSI is mapped to PUSCH (with or without ULuser data). It is therefore suggested to follow this principle forunlicensed standalone LTE.

FIGS. 12A and 12B illustrate examples of a cellular communicationsnetwork in which embodiments of the present disclosure may beimplemented. The example embodiments illustrated in FIGS. 12A and 12Bare implemented in a cellular communications network 10 (also referredto herein as a communications system). In the example of FIG. 12A, thecellular communications network 10 includes a base station 12 (e.g., aneNB in LTE terminology) serving a cell 14 operating on a carrier f₁ in alicensed frequency spectrum and a cell 16 operating on a carrier f₂ inan unlicensed frequency spectrum (e.g., the 5 gigahertz (GHz) frequencyspectrum). According to one example LAA scheme, the cell 14 isconfigured as a PCell of a wireless device 18 (e.g., an LTE UE), and thecell 16 is configured as an SCell of the wireless device 18, accordingto a CA scheme for LAA. As such, with respect to the wireless device 18,the cell 14 is referred to as the PCell 14 of the wireless device 18,and the cell 16 is referred to as the SCell 16 or, more precisely, theLAA SCell 16 of the wireless device 18.

In FIG. 12B, the cells 14 and 16 are served by separate base stations12-1 and 12-2, respectively. In this regard, the cell 16 may be astandalone LAA cell or an LAA cell utilized with respect to the wirelessdevice 18 according to a dual connectivity scheme (where the basestations 12-1 and 12-2 are connected via a non-ideal backhaul link). Thebase stations 12-1 and 12-2 are communicatively connected to a corenetwork 20 (e.g., an Evolved Packet Core (EPC)) and, in someembodiments, may communicate with one another either via abase-station-to-base-station interface (e.g., the X2 interface in LTE)or via the core network 20.

FIG. 13 illustrates the operation of the base station 12-1 (or the basestation 12-2) and the wireless device 18 to implement proposal 3 aboveaccording to some embodiments of the present disclosure. As illustrated,when utilizing asynchronous HARQ, the wireless device 18 transmits a ULtransmission for a particular UL HARQ process on the LAA cell (step100). The wireless device 18 assumes that the UL transmission wassuccessful and, as such, sets a locally maintained status for the ULHARQ process to ACK (step 102). The wireless device 18 may or may notreceive a subsequent UL grant (NDI not toggled) from the base station12-1 (or 12-2) corresponding to the UL HARQ process (step 104). In someembodiments, the UL HARQ process index is indicated in the HARQ processindex field in the UL grant. The wireless device 18 only performs HARQretransmission for the HARQ process upon reception of a corresponding ULgrant for the UL HARQ process (step 106).

FIG. 14 is a flow chart that illustrates the operation of the wirelessdevice 18 to implement proposals 4-7 above according to some embodimentsof the present disclosure. As illustrated, the wireless device 18determines whether the wireless device 18 has a valid UL grant on theLAA cell in a subframe (step 200). If not, the wireless device 18continues to monitor for a valid UL grant on the LAA cell. If thewireless device 18 has a valid UL grant on the LAA cell in the subframe,the wireless device 18 starts a UL HARQ Feedback timer for acorresponding HARQ process (step 202). The wireless device 18 thenmonitors for expiry of the Uplink HARQ Feedback timer for the HARQprocess (step 204). Once the UL HARQ Feedback timer has expired, in thisexample, the wireless device 18 starts a correspondingDRX-RetransmissionTimer and remains in the DRX Active Time as long asthe DRX-RetransmissionTimer is running (steps 206 and 208). Note thatwhile FIG. 14 utilizes both the UL HARQ Feedback timer and theDRX-RetransmissionTimer, the process may alternatively use only one ofthe two timers, e.g., the UL HARQ Feedback timer (in which case anydesired action may be performed upon expiry of the UL HARQ Feedbacktimer where this action is not limited to starting theDRX-RetransmissionTimer).

FIG. 15 illustrates the operation of the base station 12-1 (or the basestation 12-2) and the wireless device 18 to implement proposal 8 or 9above according to some embodiments of the present disclosure. Asillustrated, in some embodiments, the base station 12-1 (or the basestation 12-2) sends feedback control information to the wireless device18 to control whether HARQ feedback bundling is to be performed by thewireless device 18 for UCI (step 300). The feedback control informationmay also indicate how many HARQ feedbacks the wireless device 18 is tobundle in UCI. As indicated by the dashed line, step 300 is optional.The base station 12-1 (or the base station 12-2) transmits one or moreDL transmissions to the wireless device 18 on the LAA cell for one ormore DL HARQ processes (step 302). At some point, the wireless device 18transmits UCI (including (bundled) HARQ feedback) containing the DL HARQprocess IDs of the one or more DL HARQ processes, e.g., eitherexplicitly or as a bitmap (step 304).

FIG. 16 is a flow chart that illustrates the operation of the wirelessdevice 18 to implement proposal 11 above according to some embodimentsof the present disclosure. As illustrated, the wireless device 18determines whether the wireless device 18 has a valid UL grant on theLAA cell in a subframe (step 400). If not, in this example, the processends. If the wireless device 18 has a valid UL grant on the LAA cell inthe subframe, the wireless device 18 multiplexes pending HARQ feedback(and possibly other UCI) onto PUSCH (step 402).

FIG. 17 is a flow chart that illustrates the operation of the wirelessdevice 18 to implement proposal 12 above according to some embodimentsof the present disclosure. As illustrated, the wireless device 18determines whether the wireless device 18 has a valid UL grant on theLAA cell in a subframe (step 500). If so, in this example, the processends. If the wireless device 18 does not have a valid UL grant on theLAA cell in the subframe, the wireless device 18 sends pending HARQfeedback on (long) PUCCH upon successful short LBT (step 502).

Note that the processes of FIGS. 16 and 17 may be utilized together suchthat, if there is a valid UL grant, the wireless device 18 multiplexespending HARQ feedback (and possibly other UCI) onto PUSCH; but, if thereis not a valid UL grant, the wireless device 18 sends pending HARQfeedback on (long) PUCCH upon successful short LBT.

FIG. 18 illustrates the operation of the base station 12-1 (or the basestation 12-2) and the wireless device 18 to implement proposal 13 aboveaccording to some embodiments of the present disclosure. As illustrated,the base station 12-1 (or the base station 12-2) transmits a UL grant ora DL assignment for the LAA cell to the wireless device 18 (step 600).The wireless device 18 skips UL LBT for the LAA cell if both (1) thewireless device 18 performed a UL transmission (PUCCH or PUSCH) in thepreceding subframe and (2) the base station 12-1 (or the base station12-2) explicitly permitted skipping LBT for the LAA cell in the UL grant(for PUSCH) or DL assignment (for PUCCH) (step 602). Assuming bothconditions are true, the wireless device 18 performs the UL transmissionon the LAA cell, skipping LBT (step 604).

FIG. 19 illustrates the operation of the base station 12-1 (or the basestation 12-2) and the wireless device 18 to implement some or all ofproposals 15-17 above according to some embodiments of the presentdisclosure. As illustrated, the base station 12-1 (or the base station12-2) sends a DL assignment for a subframe on the LAA cell to thewireless device 18 and an indication that the subframe is a shortened DLsubframe (step 700). Optionally (as indicated by the dashed arrow), thewireless device 18 determines sPUCCH resources to be utilized for HARQfeedback based on, e.g., RRC configuration in combination with thereceived DL assignment (step 702). The wireless device 18 sends pendingHARQ feedback (and possibly other UCI) on sPUCCH (e.g., using thedetermined sPUCCH resources) upon receiving the indication of theshortened DL subframe (step 704).

FIG. 20 illustrates the operation of the base station 12-1 (or the basestation 12-2) and the wireless device 18 to implement some or all ofproposals 18-20 above according to some embodiments of the presentdisclosure. As illustrated, the base station 12-1 (or the base station12-2) configures the wireless device 18 with D-SR resources using, e.g.,RRC signalling (step 800). The wireless device 18 utilizes theconfigured D-SR resources (step 802). More specifically, the wirelessdevice 18 may send D-SR in those occasions on PUCCH after successful LBTand/or may send D-SR in those occasions on sPUCCH if the base station12-1 (or 12-2) announces the subframe to be a shortened DL subframe.

FIG. 21 is schematic diagram of the base station 12 in accordance withsome embodiments of the present disclosure. Note that this discussion isequally applicable to the base stations 12-1 and 12-2. The base station12 can be an LTE base station (e.g., an eNB, or a PCell base station) oranother type of base station that can communicate wirelessly with thewireless device 18 (which, in LTE, may be a UE) (e.g., an SCell radiostation operating in unlicensed spectrum). The base station 12 includesa transceiver 22, one or more processors 24 (e.g., one or more CentralProcessing Units (CPUs), one or more Application Specific IntegratedCircuits (ASICs), one or more Field Programmable Gate Arrays (FPGAs),and/or the like), memory 26, and a network interface 28. The transceiver22, which may include one or more transmitters and one or morereceivers, allows the base station 12 to send and receive wirelesssignals. The processor(s) 24 can execute instructions stored in thememory 26 based on, e.g., signals received wirelessly via thetransceiver 22. In particular, in some embodiments, the functionality ofthe base station 12 described herein is implemented in software that isstored in the memory 26 and executed by the processor(s) 24. The networkinterface 28 allows the base station 12 to interact with a core network,such as sending and receiving signals from a wired link. The basestation 12 can communicate wirelessly with one or more wireless devices18.

In some embodiments, a computer program including instructions which,when executed by at least one processor 24, causes the at least oneprocessor 24 to carry out the functionality of the base station 12 (orthe base station 12-1 or 12-2) according to any one of the embodimentsdescribed herein is provided. In some embodiments, a carrier containingthe aforementioned computer program product is provided. The carrier isone of an electronic signal, an optical signal, a radio signal, or acomputer readable storage medium (e.g., a non-transitory computerreadable medium such as the memory 26).

FIG. 22 illustrates the base station 12 according to some otherembodiments of the present disclosure. Note that this discussion isequally applicable to the base stations 12-1 and 12-2. The base station12 includes one or more modules 30, each of which is implemented insoftware. The module(s) 30 operate to provide the functionality of thebase station 12 according to any of the embodiments described herein.

FIG. 23 is a schematic diagram of the wireless device 18 in accordancewith some embodiments of the present disclosure. The wireless device 18is configured to send and receive wireless signals using resources fromthe licensed spectrum (e.g., the licensed LTE spectrum in the exampleembodiments described herein), the unlicensed spectrum, or both. Thewireless device 18 includes a transceiver 32 including one or moretransmitters and one or more receivers, one or more processors 34 (e.g.,one or more CPUs, one or more ASICs, one or more FPGAs, and/or thelike), and memory 36. The transceiver 32 allows the wireless device 18to send and receive wireless signals. The processor(s) 34 can executeinstructions stored in the memory 36 based on, e.g., signals receivedwirelessly via the transceiver 32. In particular, in some embodiments,the functionality of the wireless device 18 described herein isimplemented in software that is stored in the memory 36 and executed bythe processor(s) 34.

In some embodiments, a computer program including instructions which,when executed by at least one processor 34, causes the at least oneprocessor 34 to carry out the functionality of the wireless device 18according to any one of the embodiments described herein is provided. Insome embodiments, a carrier containing the aforementioned computerprogram product is provided. The carrier is one of an electronic signal,an optical signal, a radio signal, or a computer readable storage medium(e.g., a non-transitory computer readable medium such as the memory 36).

FIG. 24 illustrates the wireless device 18 according to some otherembodiments of the present disclosure. The wireless device 18 includesone or more modules 38, each of which is implemented in software. Themodule(s) 38 operate to provide the functionality of the wireless device18 according to any of the embodiments described herein.

FIG. 25 illustrates the operation of a wireless device in a PrimaryServing Cell (PSC) and in a Secondary Serving Cell (SSC) according tosome embodiments of the present disclosure. In the embodimentillustrated in FIG. 25, a wireless device 18 that is operating in anetwork having a primary serving cell 12-1 and a SSC 12-2 receives a DLtransmission from the PSC 12-1 (step 900). In response to receiving theDL transmission from the PSC, the wireless device 18 provides HARQfeedback to the PSC (step 902). The wireless device 18 receives a DLtransmission from the SSC 12-2 (step 904) and responds by providing aHARQ feedback to the SSC instead of to the PSC (step 906).

FIG. 26 illustrates an LBT operation (shaded portion) being performed atthe end of a subframe just prior to a UL subframe versus an LBToperation being performed at the beginning of a UL subframe according tosome embodiments of the present disclosure.

The following acronyms may be used throughout this disclosure.

-   -   μs Microsecond    -   3GPP Third Generation Partnership Project    -   5G Fifth Generation    -   ACK Acknowledgement    -   AP Access Point    -   ASIC Application Specific Integrated Circuit    -   BSR Buffer Status Report    -   CA Carrier Aggregation    -   CC Component Carrier    -   CCA Clear Channel Assessment    -   CCA-ED Clear Channel Assessment Energy Detection    -   CFI Control Format Indicator    -   CIF Carrier Indicator Field    -   CPU Central Processing Unit    -   CRC Cyclic Redundancy Check    -   CRS Cell Specific Reference Symbol    -   CSI Channel State Information    -   CSMA/CA Carrier Sense Multiple Access with Collision Avoidance    -   DCI Downlink Control Information    -   DFT Discrete Fourier Transform    -   DL Downlink    -   DMRS Demodulation Reference Signal    -   DRS Dedicated Reference Signal    -   DRX Discontinuous Reception    -   D-SR Dedicated Scheduling Request    -   eNB Enhanced or Evolved Node B    -   EPC Evolved Packet Core    -   EPDCCH Enhanced Physical Downlink Control Channel    -   FDMA Frequency Division Multiple Access    -   FPGA Field Programmable Gate Array    -   GHz Gigahertz    -   HARQ Hybrid Automatic Repeat Request    -   ID Identifier    -   IP Internet Protocol    -   LAA License Assisted Access    -   LBT Listen-Before-Talk    -   LTE Long Term Evolution    -   LTE-U Long Term Evolution in Unlicensed Spectrum    -   MAC Medium Access Control    -   MCS Modulation and Coding Scheme    -   MHz Megahertz    -   ms Millisecond    -   MTC Machine Type Communication    -   NACK Negative Acknowledgment    -   NDI New Data Indicator    -   OCC Orthogonal Cover Code    -   OFDM Orthogonal Frequency Division Multiplexing    -   PCell Primary Cell    -   PDCCH Physical Downlink Control Channel    -   PDCP Packet Data Convergence Protocol    -   PDSCH Physical Downlink Shared Channel    -   PDU Protocol Data Unit    -   PHICH Physical Hybrid Automatic Repeat Request Indicator Channel    -   PSC Primary Serving Cell    -   PUCCH Physical Uplink Control Channel    -   PUSCH Physical Uplink Shared Channel    -   RE    -   Rel-n Release n    -   RRC Radio Resource Control    -   RTT Round Trip Time    -   SCell Secondary Cell    -   SC-FDMA Single Carrier Frequency Division Multiple Access    -   SI Study Item    -   sPUCCH Short Physical Uplink Control Channel    -   SR Scheduling Request    -   SRS Sounding Reference Signal    -   SSC Second Serving Cell    -   TBCC Tail Biting Convolutional Code    -   TDD Time Division Duplexing    -   TR Technical Report    -   TTI Transmit Time Interval    -   UCI Uplink Control Information    -   UE User Equipment    -   UL Uplink    -   UL-SCH Uplink Shared Channel    -   WLAN Wireless Local Area Network

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present disclosure. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

The invention claimed is:
 1. A method operation of a wireless device ina network having a primary serving cell and a secondary serving cell,the method comprising: in response to receiving a Downlink, DL,transmission from the primary serving cell, providing a Hybrid AutomaticRepeat Request, HARQ, feedback to the primary serving cell instead of tothe secondary serving cell; and in response to receiving a DLtransmission from the secondary serving cell, providing the HARQfeedback to the secondary serving cell instead of to the primary servingcell.
 2. A method of operation of a wireless device, comprising:determining whether the wireless device has a valid Uplink, UL, grant ina subframe on a cell, the cell operating in an unlicensed frequencyspectrum; upon determining that the wireless device has a valid ULgrant, multiplexing pending Hybrid Automatic Repeat Request, HARQ,feedback onto a UL shared channel; and upon determining that thewireless device does not have a valid UL grant, sending pendingDownlink, DL, HARQ feedback on a UL control channel upon a successfulshort Listen-Before-Talk, LBT, operation.
 3. The method of claim 2wherein the uplink control channel is a long uplink control channel. 4.A method of operation of a wireless device, comprising: skipping Uplink,UL, Listen-Before-Talk, LBT, before a UL transmission in a subframe on acell operating in an unlicensed frequency spectrum in response to thewireless device performing the UL transmission in a preceding subframeand receiving an explicit indication that skipping the UL LBT ispermitted; wherein the UL transmission in the preceding subframe was aPhysical Uplink Shared Channel, PUSCH, or a Physical Uplink ControlChannel, PUCCH.
 5. The method of claim 4 wherein the UL transmission inthe preceding subframe was a Physical Uplink Shared Channel, PUSCH,transmission.
 6. The method of claim 4 wherein the UL transmission inthe preceding subframe was a long Physical Uplink Control Channel,PUCCH, transmission.
 7. A method of operation of a wireless device,comprising: performing an Uplink, UL, Listen-Before-Talk, LBT, operationat a beginning of a UL subframe rather than at the end of a precedingsubframe; and not performing the UL LBT prior to the beginning of the ULsubframe.
 8. A method of operation of a wireless device, comprising: inresponse to the wireless device receiving an indication of a shortenedDownlink, DL, subframe, sending pending Hybrid Automatic Repeat Request,HARQ, feedback on a short Uplink, UL, control channel on a celloperating in an unlicensed frequency spectrum; wherein the wirelessdevice does not need to perform Listen-Before-Talk, LBT, prior tosending the pending HARQ feedback on the short UL control channel.
 9. Amethod of operating a wireless device, comprising: determining that thewireless device has a valid Uplink, UL, grant; starting an UL HybridAutomatic Repeat Request, HARQ, feedback timer in a subframe of an ULtransmission that corresponds to the UL grant; and starting aDiscontinuous Reception, DRX, retransmission timer upon expiration ofthe UL HARQ feedback timer.
 10. The method of claim 9, furthercomprising remaining in DRX active time as long as the DRXretransmission timer is running.
 11. A wireless device, comprising:processing circuitry and memory collectively configured to: determinethat the wireless device has a valid Uplink, UL, grant; start an ULHybrid Automatic Repeat Request, HARQ, feedback timer in a subframe ofan UL transmission that corresponds to the UL grant; and start aDiscontinuous Reception, DRX, retransmission timer upon expiration ofthe UL HARQ feedback timer.
 12. The wireless device of claim 11, whereinthe processing circuitry and memory are further configured to remain inDRX active time as long as the DRX retransmission timer is running. 13.A method of operation of a wireless device, comprising: in response tothe wireless device receiving an indication of a shortened Downlink, DL,subframe, sending pending Hybrid Automatic Repeat Request, HARQ,feedback on a short Uplink, UL, control channel on a cell operating inan unlicensed frequency spectrum; and determining short UL controlchannel resources on which to send the pending HARQ feedback.
 14. Themethod of claim 13 wherein the wireless device determines the short ULcontrol channel resources based on the Radio Resource Control (RRC)configuration and information contained within a DL assignment.